1. Field of Invention
This invention relates to flame-proofing of shingled surfaces and, in particular, to a method of treating wood shingled surfaces to impart flame resistance thereto.
2. Brief Statement of the Prior Art
Flame-proofing treatments of wood have generally used intumescent compositions such as tri-ammonium phosphate, polyhydric alcohols and mitrogenous materials. Upon exposure to the flame, the ammonium phosphate decomposes, absorbing heat to decrease the temperature of the coated item. Frequently, the gases released from intumescent coatings are toxic.
Halogenated polymers have also been used as flameproofing agents and are applied by pressure impregnation, a costly method. Bromine and chloride are most commonly used in epoxy polymers, polyesters and vinyl polymers. Additionally, inorganic materials such as zinc borate and antimony oxides are added to decrease the flammability of the coatings. As with intumescent coatings, these halogenated polymer coatings also release highly toxic gases. Flame resistance of wood substrates has also been achieved to some degree by pressure impregnation of wood with silicates, phosphates and borates. The flame resistance achieved with these treatments is not entirely permanent as the materials are lost from the substrate upon weathering, and this loss is particularly acute with topically applied coatings which lack the limited degree of permanency of impregnated coatings. Additionally, toxicity of the decomposition products can be a problem with these flame retardants also.
Alumina trihydrate is an ideal material for achieving flame retardancy since it releases water vapor when heated above about 280 degrees F. This water vapor release absorbs heat from the advancing flame and protects the substrate. Heretofore, however, there has been no coating developed which traps the water vapor released from alumina trihydrate to form a foam which contains the water vapor and pyrolysis gases beneath a refractory and thermal insulating barrier over the wood substrate.
In my aforementioned parent application, I have disclosed a flame-proofing composition which is a mixture of a thermoplastic, ambient-temperature film former such as a latex polyvinyl acetate, alumina trihydrate and an inorganic fiber filler such as glass fibers.
A major problem in fire retardant systems for wood shake or shingle roofs is flame penetration through "breathing" of the roof. Typical home applications of shake or shingles are installed for esthetic reasons. Particularly with wood shake, under the dual attack of flame and wind, the flames can be driven beneath the shingles and can initiate combustion of the undersurface of shingles which are only treated on their exposed surfaces, or of the underlayment, which is often of a quite flammable material, e.g., tar, asphalt and resin impregnated paper.